6c. Clematis Subg. Atragene (Linnaeus) Torrey & A. Gray, Fl. N. Amer. 1: 10. 1838.
Atragene Linnaeus, Sp. Pl. 1: 542. 1753; Gen. Pl. ed.5, 241. 1754
Woody vines or rhizomatous herbs with short, tufted stems. Leaf blade 1-3-ternate, lobed or unlobed, margins entire or coarsely serrate. Inflorescences terminal on short shoots or rarely terminal on long shoots, 1[-2]-flowered with bractless peduncles subtended by 1 or 2 pairs of leaves. Flowers bisexual, ± nodding; perianth widely bell-shaped to rotate; sepals ascending or tardily spreading, not connivent, usually violet-blue, sometimes reddish violet, or white, ovate to oblong, thin, margins densely pubescent, abaxially sparsely pubescent; staminodes present between stamens and sepals, flattened, petaloid, bearing reduced, sterile anthers; filaments flattened, pubescent at least on margins. Achenes flattened; beak over 2 cm, plumose.
Species ca. 5 (2 in the flora): temperate to subarctic and subalpine North America and Eurasia.
F. B. Essig (1992) suggested that Clematis subg. Atragene might be included in Clematis subg. Clematis . Because of its distinctive inflorescence and floral morphology, however, and because it has not been successfully crossed with species in any other subgenus, its subgeneric status is retained here.
The two North American species have been known to hybridize in Montana.
Pringle, J. S. 1971. Taxonomy and distribution of Clematis, sect. Atragene (Ranunculaceae), in North America. Brittonia 23: 361-393.